Zellix, Sanity Flayer + Haunted One + Pith Driller + Krark-Clan Ironworks + Faces of the Past

Zellix, Sanity Flayer

Haunted One

Pith Driller

Krark-Clan Ironworks

Faces of the Past

How it works

1. Activate Zellix by paying 1 and tapping it.
2. Haunted One triggers, causing all Horrors you control to get +2/+0 and undying until end of turn.
3. Resolve the Zellix ability, causing a player to mill three cards.
4. If the player milled a creature card this way, Zellix triggers, creating a 1/1 Horror creature token.
5. Activate Krark-Clan Ironworks by sacrificing Pith Driller, adding CC.
6. When Pith Driller dies, its undying ability and Faces of the Past trigger.
7. Resolve the Pith Driller trigger, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
8. When Pith Driller enters the battlefield, it triggers, putting a -1/-1 counter on it.
9. Resolve the Faces of the Past trigger, untapping all Horrors.
10. Repeat.

This elegant loop transforms the humble Horror creature type into a self-sustaining engine by tying together death, rebirth, and untapping. With Haunted One granting your creatures undying whenever they become tapped, and Zellix, Sanity Flayer's activated ability tapping itself to mill cards and spawn Horror tokens, you have all the pieces needed to keep the cycle spinning. As you sacrifice Pith Driller to Krark-Clan Ironworks for mana, its death triggers both its own undying return and Faces of the Past, which untaps your Horrors so Zellix can mill again and trigger Haunted One all over again. The -1/-1 counter from Pith Driller's entry neatly cancels out the +1/+1 counter from undying, ensuring the whole apparatus can repeat indefinitely for infinite mana, triggers, and tokens.